Metal-to-ceramic seal



Sept. 1, 1953 K. H. MCPHEE ET AL 2,650,683

METAL-TO-CERAMIC SEAL Filed Nov. 3, 1949 2 Sheets-Sheet l INVENTORS A EA /VHH H. Ma /v55 fi/wxzy W. 50052575014 Sept. 1, 1 3 Y K. H. MOPHEE ET AL 2,650,683

METAL-TO-CERAMIC SEAL Filed No v. 5. 1949 2 Sheets-Sheet 2 JNVENTORS KENNETH /7f Ma PHEE /5 /meev Ml 0D5STEOM AUae/vm UNITED STATES ZF'ECIE METAL-TO-CERAMIC SEAL Kenneth H. McPhee and Harry W. Socierstrom, Cedar Rapids, Iowa, assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of-Iowa Application November 3, 1949, Serial No. 125,354

8 Claims. (Cl. 189--'36.5)

T OFFICE This invention relates to the art of vacuurn- A still further feature relates to thenovel'ortight sealing, and more especially to seals for gani-zation, arrangement andrelative location and highly evacuated devicessuoh as electron tubes teroonnection of partswhich cooperate to proand the like. vicle an hnproved metal-to-ceramic sealed joint.

A principal object of the invention is to pro- 9 in therlraWin-g \vh'ch is illustrative ofone previde an improved vacuum-tight bond or seal beferred embodiment, tween metal and ceramic members. Fig. i is a perspective anzlpartly sectional view Another object is to provide a novel arrangeof a sealed joint according to the invention. ment for inte 'rally bonding a tubular insulator Fig. 2 is a portion of an enlarged central secineinber, for example a ceramic, to a metal memtion of 1. be: through the intermediary of a novel sealing 3 is a further enlarged View of part of ring. Fig. 2.

Afeature of the invention relates to a metal- Fig. 4 is an eyploclecl viev showing the manner to-cerarnic seal for evacuated devices, wherein a N of assembly of theparts of-the joint. 110%: ote-1 S li ring is emhloyed, e b de g. 5 is a generalized external View of a typical .ic and k .g ring being supported on a rec-tron discharge tube embodyinga sealed joint separate member which takes the variaccording to the invention.

ous thrusts e erteci on the ceramic and sealing Referring to Figs. 1 to 4 there is shown one s, While her hitting the ceramic and. ring o typical form of sealed joint according to the ove p pendicular directions in respo to 29 invention. This joint may comprise-a cylindrical heat without destroying the efiectiveor tubular ceramic body It having smooth fiat of the seal. end walls H, 52. The lower end of body on nether f ure rel tes to a novel v uumthe outeroylinolrical surface and on the flat face t it sealing r n m w en a tubular is, is provided with a metallizecl coating 13 (see c ramic member a d metal disc-like member, Fig. 4) which may be appliedby spraying, coating w--erein the ceramic member is bonded to a dipping, brushing, etc. lhis metallized coating specially shaped flexible metal sealing ring havmay be of any well-known type, for example ing an outer peripheral flange which is sealed copper, brass, solder, silver, etc.,\vh ch is capable to the said metal member, and an inner peripherf being easily Wet when in contact with a a1 flange which is in slidable engag nt W t melted. brazing or soldering material. While Fig. & Separate ppo t ring which is sandwiched be- 1 shows a seal only at the lower end of member tween the said inner flange and said clismlike til, it will beunderstoosl that, if desired, a similar member. seal may he provided at the upper end. The

Another feature relates to a novel metal-toceramic member is is arranged. to be vacuums i e p y a l s n which h tight sealed to a metal base or disc-like member inner and outer margins or flanges, and with gig. h may b unperfo ated vjhigh may have an intervening section having a portion bent back a central Opening, as indicated by the dot dash upon itself, the inner margin of the sealing ring lines in Land as indicated in section in Fig. bonded. to the end of the ceramic member, The member which may for example be the outer margin of the sealing ring being of (Zapper, has a mam relatively Wide annular 339115433. 0 member of Seal. groga upper face and a pair of outer further feature rela esto a novel metal sealcongentric but narrower annular gmoves 5 gr ing ring for evacuated devices such as electron Sea-(38d in grows 55 is a ring is of Stainless Steel 1% es and the like. or similar hard metal or alloy wl'iich is not read- 1 further if: lle relates 136 a sealed. 301111, be- 11y wettable and does n01; bond to the usual on a tubular ceramic body and a metallic brazing or soldering materials. Preferably, aldisc-lilze memb pa t u y s l in on thou h not necessarily, the ring I8 has a thickevacuated electron discharge device. The joint 1135s which is ubstantially the same as the depth according to the invention has a novel arrangef grgove i5 and has a radial Width which is merit of rings whereby one ring functions primaterially less than the width of groove !5. For marily as an expansible sealing member, while example, the width-of ring it may be approxithe other ringserves to provide the required suplnately one-half the Width of the groove I5. Ring port and mechanical'strength to the seal to resist it is p d With a 881465 f uc ic ess the pressure of the outside atmosphere when the reduces-Width sections l9 for purposes to be device is highly evacuated. described. The ring i8 preferably has an internal diameter which is slightly greater than the diameter of the inner wall 20, so as to freely seat within the groove l5. For providing the necessary vacuum-tight seal, there is an annular sealing ring 2| having an outer flat margin 22 with a downwardly extending lip 22a, and a coplanar inner flat margin 23. These two margins are joined by an integral and doubly bent-back section 2 having a central vertically fiat portion 25 which is adapted to seat against the metallized periphery l3 of the ceramic member H]. The downwardly bent portion 26 is formed so that it is at right angles to the inner margin 23, and the width of this bent-back portion is such that when the ring 2| is mounted on the ring I8, as shown in Figs. 1, 2 and 3, the vertical section 25 presses tightly against the peripheral surface of member Hi. Before assembly of the ceramic member In within the vertically-bent portion of ring 2|, a ring 21 (see Fig. 4) of solder, brass, nickel, or other similar material is dropped into the channel 28. Likewise, before placing the ring 2| on the base l4, another ring 29 of solder, brass, nickel, or other brazing alloy, is dropped into the groove IS. The parts assembled in the relation shown in Figs. 1 to 3, are placed into a suitable furnace, and heated sufficiently to melt the rings 2! and 29. By capillary action, the molten soldering or brazing material seeps between the metallized peripheral face of member Hi and the fiat wall 25 of ring 2|, and it also seeps etween the metallized fiat end wall I2 of member IE] and the fiat inner margin 23 of ring 2|. The assembly is then removed from the furnace and allowed to cool, whereupon the molten soldering or brazing material hardens and forms a vacuum-tight seal between the parts. If desired, an additional ring of solder or brazing material can be dropped into the groove I1, and it can be melted or brazed in a similar manner to that described above. If desired, the lip 220. can be spun downwardly after assembly, or it can be formed as an integral downward lip prior to assembly of the disc 2| with ring member I4.

- During the brazing or soldering operation, the ring It) does not become wet by the soldering or brazing material, and no permanent bond is effected between the ring 2| and the ring I8. This is necessary since the ring l8 performs the function merely of carrying all the stresses that may be exerted on the bond as a result of outside atmospheric pressure when the joint forms part of an evacuated receptacle. In such evacuated devices, the ceramic-to-metal seals are subject to very little forces of tension since because of the outside atmospheric pressure they are always under compression. However, because of the particular characteristics of the sealing ring 2| and its bonding to the ceramic l0, and because of the use of a separate unbonded thrust-taking ring IS, the sealed joint is capable of expansion and contraction without in any way affecting its sealing qualities. When the joint becomes heated for any reason during use, the metal base or member l4 expands faster than the ceramic In. However, since the ring I8 is free and not bonded to the ring 2| or to the base l4, relative motion may occur between base I4 and the ceramic i0, but Without destroying in any Way the seal between the ceramic Ill and the rin 2|. Likewise, on cooling and contracting of the joint, relative motion may occur between the ceramic and the base I l without affecting the sealing qualities of the joint. When the sealed joint forms part of the evacuated space of an electron discharge device, or the like, the channels formed by the cut-away portions IQ of ring I8 provide free passages between the interior of the device and the groove I5, thus facilitating evacuation of the device and preventing entrapped air from staying in the groove l5 subsequent to sealing.

It is believed that the manner of assembly of the parts to form the joint will be clear from the foregoing description, particularly with reference to the exploded view of Fig. 4. To assemble the parts, the ring I8 is first placed within the groove 5 in base member M. The solder or brazing ring 2'1 is then dropped into the channel 26, and the additional solder or brazing ring 29 is dropped into groove IS. The sealing ring 2| is then assembled on member l4 and ring i8, and if desired, the outer margin of ring 2| can be spun downwardly into groove N. If desired, an additional solder or brazing ring can be dropped into groove ii. The ceramic member I4 is then assembled with its fiat end |2 in engagement with the inner fiat margin 23 of ring 2|, and with its outer metallized periphery IS in engagement with the vertical bent-back portion 25. The assembly is then heated in any convenient manner to melt the various solder or brazing rings as above described, and the joint is then allowed to cool to allow the molten brazing or soldering material to harden.

While the joint according to the invention is not limited to any particular kind of evacuated device, there is shown in Fig. 5, in generalized form, an electron discharge tube having a thermionic electron emitting cathode 38, electron permeable grids 3|, 32, and an anode 23. The cathode 33 may be of any well-known type, such for example as disclosed in application Serial No. 28,984, filed May 25, 1948, now Patent No. 2,510,171, issued June 6, 1950, consisting of a plurality of radially-extending filament or cathode strips which are bridged across a central metal member 34 and a spaced surrounding metal member 35. The metal member 34 is connected to a suitable metal sleeve 36 which connects all the inner ends of the filament sections together in parallel, and the outer ends of these sections are connected in parallel by the member 35, thus enabling heating current to be supplied to the filament. The membe' 36 may be carried by a metal disc 3'! which is similar to member l4 and which is sealed to a tubular ceramic member 38 by a sealing ring 2|a similar to ring 2|, such as illustrated in Figs. 1 to 4. Likewise, the anode 33 can be attached to a metal disc 39, which disc can be similar to disc l4 and sealed to a tubular ceramic member 40 by a sealing arrangement 2|b, such as illustrated in Figs. 1 to 4.

The member 35 can be integrally united to form part of the metal disc 4| which is similar to disc l4, except that it has sealing grooves on opposite faces thereof, so that this disc 4| can be sealed to the ceramic 33 as above described, and can also be sealed to another tubular ceramic member 42. Likewise, the grid 3| can be mounted in an annular metal disc 43 carrying sealing grooves on opposite faces and respective sealing rings 2| 0, 2| d, therein, so that this disc can be sealed to ceramic 42 and to ceramic 44. Similarly, the grid 32 can be carried by a metal disc 45 which is sealed to the ceramic 44 and to the ceramic 40 in a similar manner. It will be understood, of course, that the showing of Fig. 5 is merely a generalized or schematic showing of one array of electrodes within an evacuated device, a wall or envelope portion of which is constituted mainly of ceramic and the connections to the various electrodes of which are eifected by the various disc-type seals above noted. A typical tube of this type is known in the art as a Resnatron. It will be understood, however, that the invention is not limited to any particular design of electron tube or other evacuated device, but is capable of use in any situation Where a vacuum-tight seal is to be provided between a metal member such as a metal disc and a ceramic or other insulating tubular member.

While one particular embodiment has been disclosed herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A sealed joint for evacuated devices, comprising a tubular insulator having an annular end face at one end which is substantially fiat, a metal member, and means sealing said metal member to said end of the tubular insulator, said means including a metal sealing ring having inner and outer flat portions joined by an intervening flexible portion extending at substantially right angles to said flat portions, the inner fiat portion of said sealing ring being in contact with the fiat face at the end of said insulator and said intervening portion being in contact with the peripheral end of said insulator, sealing material between said sealing ring and said end of said insulator, and a separate rigid ring located between the said flat end face of said insulator and said metal member receiving the end thrust between said insulator and said metal member in response to temperature changes in said insulator while allowing said intervening portion to flex.

2. A sealed joint according to claim 1 in which said intervening portion of said sealing ring is reversely bent with respect to said flat portions 6 rendering said sealing ring flexible in the region where it is sealed to said insulator.

3. A sealed joint according to claim 1 in which said metal member has an annular groove and said sealing ring has a section of said intervening portion in the form of a trough located in said groove, and said separate rigid ring is located between said trough and the inner wall of said annular groove.

4. A sealed joint according to claim 3 in which the said separate rigid ring is unbondcd to said first-mentioned sealing ring.

5. A sealed joint according to claim 4 in which said separate rigid ring has a plurality of transverse grooves providing communication between the sections of said annular groove located on opposite sides of said trough.

6. A sealed joint according to claim 5 in which said separate rigid ring is of a metal which is not readily wet by said sealing material.

7. A sealed joint according to claim 6 in which said separate rigid ring is of stainless steel.

8. A sealed joint according to claim 1 in which the said outer flat portion of said sealing ring is soldered to said metal member.

KENNETH H. MCPHEE. HARRY W. SODERSTROM.

References Cited in the file of this patent UNITED STATES PATENTS 

